As a result of the 'PDP activation' procedure, the GGSN assigns the 'PDP context' an IP address. The 'PDP address' is the IP of the 'PDP context'.
The 'PDP address' may be 'Dynamic', or 'Static' .
Dynamic PDP address
The GGSN assigns a dynamic IP to the 'PDP context' from a pool of IP addresses exist on the GGSN.
For every APN, there is an IP pool, (group of IPs), that exist on the GGSN. The GGSN will assign one of those IPs to the 'PDP context' in the procedure of 'PDP context activation'.
The procedure of the address assignment will be as following,
- In the 'Active PDP context request', and 'create PDP context request' respectively, The MS, and the SGSN, will put the IP address as '0.0.0.0'.
- Then, the GGSN will assign an IP address to the 'PDP context', and put the assigned IP in 'create PDP context response' message sent to the SGSN.
- Then the SGSN will give the IP to the MS in the 'Active PDP context accept' message.
Static PDP address
- The Static IP address exist in the subscription data of the MS in the HLR. Also, it exist on the SIM card memory exist in the MS.
- Therefore, the MS will request to take this static IP address in the 'Active PDP context request' sent to the SGSN.
- Then, the SGSN will compare the this IP to the subscription information for this MS received from the HLR.
- If the SGSN found that the MS has requested a valid IP, the SGSN will forward the request to the GGSN in the 'create PDP context request' message.
- Then the GGSN assigns this static IP to the 'PDP context', and replies the SGSN.
- The SGSN will forward this IP to the MS in 'Create PDP context accept' message.